X-ray radiography applied to the non-invasive inspection of the contents of containers is a mature technology carried out by a wide variety of methods. An early purpose of x-ray radiography was to produce a high resolution projected image for visual inspection of the contents. In the past decade, as the purposes of the inspection have become targeted to finding specific contraband such as drugs and explosives, methods of dual energy and backscatter radiography have been developed to measure the atomic number of the objects, as have tomographic techniques to measure the density of the objects and coherent scattering methods to measure the crystalline properties of objects. None of these advances have measured the masses of the objects inside the containers.
There are many instances where it is important to determine, in a non-invasive way, the mass of an object inside a container. For example, the U.S. Customs needs to verify that a container shipped into this country contains the goods described by the container manifest. Because it is impractical to open and examine even a fraction of the millions of containers that enter the country every year, the U.S. treasury loses considerable revenue from high-duty goods that are declared to be low-duty items. The manifest of a container lists the contents by description and weight. It is one purpose of this invention to provide a on-destructive means of verifying that the weights of the items in the container are those declared on the manifest. The invention for measuring masses can be an integral part of the well-used technique of dual-energy analysis so that both the mass and the atomic number of objects can be measured simultaneously to give additional information to compare with the manifest or to find contraband.